1. Field of the Invention
The present invention relates to a method of purifying organic impurities contained in the used cyclotron target water and an apparatus for the same, and more particularly, to a method for removing the organic impurities in the used O-18 enriched cyclotron target water contaminated during radioisotope F-18 production by using UV radiations generated from the low pressure mercury (Hg) lamp and catalytic photo-reaction of dissolved oxygen (DO) and an apparatus employing the method.
2. Description of the Related Art
In general, the present invention relates to purification of the organic impurities contained in the used cyclotron target water and its apparatus. More specifically, this invention is focused on purifying technique and its apparatus for removing the organic impurities in the used O-18 enriched cyclotron target water contaminated during radioisotope F-18 production by using UV radiations generated from the low pressure Hg lamp (L-lamp hereafter) and catalytic photo-reaction of dissolved oxygen (DO).
Oxygen isotope consists of 99.76% of O-16, 0.04% of O-17, and 0.2% of O-18 in nature. O-18 enriched water (>90%) is used as a target in a cyclotron for production of the β-emitting radioisotope F-18 (half-life=109.7 min) under O-18(p,n)F-18 reaction. F-18 is essential for PET (Positron Emission Tomography) pharmaceutical [F-18]-labeled 2-deoxyglucose (FDG) synthesis. Since O-18 is very expensive and the demand for O-18 stable isotope increases as the superior tumor diagnostic feasibility obtained from PET increases, it is important to re-use the cyclotron target again.
After the O-18 enriched target water is irradiated by protons in a cyclotron, it contains various organic substances such as acetone (CH3COCH3), ethanol (CH3CH2OH), methanol (CH3OH), and acetonitrile (CH3CN), etc. which are contaminated during the F− ion separation and target cleaning processes. These organic impurities may increase the target vapor pressure and decrease the target life-time as a result. More importantly, they inhibit the separation of the generated −F ions in the target medium after proton irradiation. The concentration of the organic impurities must be maintained below 10 ppm to be used in a cyclotron again. This is why those organic impurities in the target must be removed before it is used again.
Oxidation of organics by UV irradiation is known as the most popular processes for removing the organic substances contained in an aqueous solution. However, O-18 water purifier that uses only UV irradiation may not be applicable for purification of O-18 enriched target water since its purifying efficiency is very low.
While an advanced oxidation process which combines UV irradiation with catalysts such as H2O2, O2, O3 and TiO2 has been widely applied for removing organic materials in an aqueous solution, UV irradiation process with catalysts must be applied cautiously for the remediation of the cyclotron target water whose purity should remain as it was. It is because sometimes more difficult to remove the remaining catalysts and the newly produced products in the medium after the catalytic reaction of the purification process.
It is also important for the purification scheme to recover the purified target water as much as possible while the concentration of O-18 in the water should be maintained as high as possible.
Even though a commercial O-18 target water purifier developed by SUMITOTO from Japan is sufficient in the degrees of purification and also recovery, the price of the equipment is very high and the quantity of the sample that can be purified during a day is limited. Also the purification process is complicated since it uses UV irradiation together with cold distillation.
Hence, the technique and apparatus, which can purify the organic impurities in the sample to below 10 ppm while more than 98% of the initial samples in average can be collected after the process at the same time, are necessary.